The current wireless local area network (WLAN) Authentication, Authorization, Accounting (AAA) solutions do not provide adequate support for WLAN operators to maintain business relationships with multiple virtual operators, and in particular, with respect to management of session keys used for WLAN access. Failure to properly control and mange the session keys could result in potential security and management problems.
WLANs are increasingly being deployed in hot spots such as hotels, airports and cafés. A sound and efficient AAA (Authentication, Authorization, Accounting) solution would be of great importance for enabling secure public wireless LAN access. In particular, such an AAA solution should be able to support a virtual operator concept in which third party providers such as ISPs, cellular operators and pre-paid card providers offer AAA services to the public WLANs and the wireless users. This way, wireless users do not have to open an account or pay by credit each time they go to a different hot spot; instead, they can use existing ISP accounts, cellular accounts or a pre-paid card purchased anywhere to gain access to the public WLAN. This could significantly increase the business opportunities for the WLAN operators as well as third party virtual operators. However, the current wireless LAN access solutions are all designed for local set-ups such as a corporate environment in which only a single authentication server is used. For example, the IEEE 802.11 standard body chooses IEEE 802.1x as the solution for WLAN access control, and the current usage models use authentication servers to control session key assignments. While this is sufficient for a corporate environment or the like, it is certainly problematic in a public hot spot where multiple authentication servers belonging to different business entities may coexist. It is very difficult, if at all possible, for these authentication servers to coordinate key assignments for an access point.
Current key distributions will now be described. In one scenario, a mobile user in a public WLAN hot spot does not have a prior trust relationship with the WLAN access point. The user intends to use a third party service provider (e.g. an Internet service provider (ISP)) as a trust bridging entity. A service provider may be referred to as a virtual operator. The user maintains an account with this virtual operator, which has a business relationship with the WLAN operator. Because the user has an established trust relationship with the virtual operator, she is able to authenticate herself with the virtual operator in a secure manner. The virtual operator then securely transmits a session key to the user as well as the WLAN access point (because the virtual operator also has a trust relationship with the WLAN). Because of this shared session key, the wireless LAN then knows that the user is authorized to access the network and thus grants access to the user. Note that in this scheme, the virtual operator assigns the session key since it has a trust relationship with both the user and the WLAN.
The session key is used for local access and should be local to the WLAN access point, e.g., assigned and maintained by the access point. When multiple virtual operators are present, the above mentioned key management scheme is problematic in at least two areas. First, for the virtual operator, it is often problematic to assign and manage session keys for tens of thousands of access points belonging to different entities, that is, to accommodate different encryption algorithms and key lengths for different types of access points. Secondly, for the access point, it may be difficult to make sure that multiple virtual operators assign session keys in a consistent manner, e.g. it has to make sure two users are not using the same key assigned by two different virtual operators at the same time.
A key difficulty is that the access point does not share a secret with the wireless user, thus it is not secure to directly send a session key from the access point to the user. In one solution to this problem is that the virtual operator notifies the access point (AP) about the user's public key upon successful user authentication. The AP then encrypts the session key using the user's public key and then sends the result to the user. Since only that specific user is able to decrypt the session key using her corresponding private key, the session key can be securely established between the AP and the wireless user. However, this scheme requires the use of public/private keys, which may not be compatible with the actual authentication methods between the wireless user and the authentication server. It is likely that the user has to maintain two different types of keys (private key for decrypting session key and password type of key for authenticating with the authentication server). This not only increases the client software complexity, but also increases the difficulty in securely maintaining keys. Further, this scheme does not work with IEEE 802.1x, which is becoming a standard in WLAN security.
Therefore, a need exists for a solution in which keys are locally assigned and managed by an access point, yet wireless users are able to securely obtain session keys without a prior trust relationship with the access point.